During the taxiing phases which precede takeoff or which follow landing, the pilot steers the aircraft by following a path, generally materialized by a line painted on the ground. During these taxiing phases, the pilot must avoid moving outside of the taxiways so as not to take the risk of getting bogged down or stuck in the verges.
The path followed by the pilot generally comprises changes of direction which are difficult maneuvers to carry out because the pilot has a reduced field of vision through the windscreen of the aircraft and because this field of vision is distant from the position of the wheels of the aircraft.
Thus, when the pilot observes a change of direction through the windscreen, he must wait before initiating the corresponding change of direction control and he must delay this control in time in such a way that the wheels follow the path correctly. Generally, when the pilot initiates the change of direction control, he can no longer see the portion of the path which includes this change of direction.
The time delay of the change of direction control varies from one aircraft to another, notably as a function of the dimensions of the aircraft.
Although the pilot has a maneuvering margin for small-sized aircraft, this margin is reduced for large-sized aircraft and a trajectory deviation can lead to an exit from the taxiway if the latter is narrow.